ORCID Profile
0000-0002-0897-4884
Current Organisation
Ruhr-Universität Bochum
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Publisher: Elsevier BV
Date: 08-2013
Publisher: Springer Science and Business Media LLC
Date: 23-10-2017
DOI: 10.1038/NGEO3048
Publisher: Elsevier BV
Date: 09-2015
Publisher: European Association of Geochemistry
Date: 09-2018
Publisher: European Association of Geochemistry
Date: 11-2017
Publisher: Elsevier BV
Date: 04-2017
Publisher: Springer Science and Business Media LLC
Date: 06-2016
Publisher: Elsevier BV
Date: 03-2017
Publisher: Elsevier BV
Date: 10-2015
Publisher: Elsevier BV
Date: 10-2015
Publisher: Elsevier BV
Date: 08-2013
Publisher: Springer Science and Business Media LLC
Date: 25-07-2017
Publisher: Elsevier BV
Date: 10-2014
Publisher: Springer Science and Business Media LLC
Date: 23-12-2020
DOI: 10.1007/S00410-020-01756-3
Abstract: The Izu–Bonin–Mariana volcanic arc is situated at a convergent plate margin where subduction initiation triggered the formation of MORB-like forearc basalts as a result of decompression melting and near-trench spreading. International Ocean Discovery Program (IODP) Expedition 352 recovered s les within the forearc basalt stratigraphy that contained unusual macroscopic globular textures hosted in andesitic glass (Unit 6, Hole 1440B). It is unclear how these andesites, which are unique in a stratigraphic sequence dominated by forearc basalts, and the globular textures therein may have formed. Here, we present detailed textural evidence, major and trace element analysis, as well as B and Sr isotope compositions, to investigate the genesis of these globular andesites. S les consist of $$\\hbox {K}_2\\hbox {O}$$ K 2 O -rich basaltic globules set in a glassy groundmass of andesitic composition. Between these two textural domains a likely hydrated interface of devitrified glass occurs, which, based on textural evidence, seems to be genetically linked to the formation of the globules. The andesitic groundmass is Cl rich (ca. $$3000\\, \\mu \\hbox {g/g}$$ 3000 μ g/g ), whereas globules and the interface are Cl poor (ca. $$300\\, \\mu \\hbox {g/g}$$ 300 μ g/g ). Concentrations of fluid-mobile trace elements also appear to be fractionated in that globules and show enrichments in B, K, Rb, Cs, and Tl, but not in Ba and W relative to the andesitic groundmass, whereas the interface shows depletions in the latter, but is enriched in the former. Interestingly, globules and andesitic groundmass have identical Sr isotopic composition within analytical uncertainty ( $$^{87}\\hbox {Sr}/^{86}\\hbox {Sr}$$ 87 Sr / 86 Sr of $$0.70580 \\pm 10$$ 0.70580 ± 10 ), indicating that they likely formed from the same source. However, globules show high $$\\delta ^{11}$$ δ 11 B (ca. + 7 $$\\permille$$ ‱ ), whereas their host andesites are isotopically lighter (ca. – 1 $$\\permille$$ ‱ ), potentially indicating that whatever process led to their formation either introduced heavier B isotopes to the globules, or induced stable isotope fractionation of B between globules and their groundmass. Based on the bulk of the textural information and geochemical data obtained from these s les, we conclude that these andesites likely formed as a result of the assimilation of shallowly altered oceanic crust (AOC) during forearc basaltic magmatism. Assimilation likely introduced radiogenic Sr, as well as heavier B isotopes to comparatively unradiogenic and low $$\\delta ^{11}\\hbox {B}$$ δ 11 B forearc basalt parental magmas (average $$^{87}\\hbox {Sr}/^{86}\\hbox {Sr}$$ 87 Sr / 86 Sr of 0.703284). Moreover, the globular textures are consistent with their formation being the result of fluid-melt immiscibility that was potentially induced by the rapid release of water from assimilated AOC whose escape likely formed the interface. If the globular textures present in these s les are indeed the result of fluid-melt immiscibility, then this process led to significant trace element and stable isotope fractionation. The textures and chemical compositions of the globules highlight the need for future experimental studies aimed at investigating the exsolution process with respect to potential trace element and isotopic fractionation in arc magmas that have perhaps not been previously considered.
Publisher: Elsevier BV
Date: 11-2017
Publisher: Springer Science and Business Media LLC
Date: 08-07-2020
Publisher: Springer Science and Business Media LLC
Date: 13-09-2021
Publisher: Geological Society of America
Date: 05-2013
DOI: 10.1130/G34066.1
Publisher: Springer Science and Business Media LLC
Date: 06-09-2013
DOI: 10.1038/NCOMMS3405
Publisher: Wiley
Date: 25-10-2013
DOI: 10.1111/IJAG.12046
Publisher: European Association of Geochemistry
Date: 09-2018
Publisher: Elsevier BV
Date: 06-2008
Publisher: Springer Science and Business Media LLC
Date: 31-10-2014
Publisher: Elsevier BV
Date: 11-2017
Publisher: Elsevier BV
Date: 08-2007
Publisher: Elsevier BV
Date: 05-2016
Publisher: Springer Science and Business Media LLC
Date: 28-03-2015
Publisher: Elsevier BV
Date: 10-2016
Publisher: Springer Science and Business Media LLC
Date: 28-02-2021
DOI: 10.1007/S00410-020-01769-Y
Abstract: Equilibria between Ti oxides and silicate melt lead to Ti isotope fractionation in terrestrial s les, with isotopically light Ti oxides and isotopically heavy coexisting melt. However, while Ti is mostly tetravalent in terrestrial s les, around 10% of the overall Ti is trivalent at f O 2 relevant to lunar magmatism (~ IW-1). The different valences of Ti in lunar s les, could additionally influence Ti stable isotope fractionation during petrogenesis of lunar basalts to an unknown extent. We performed an experimental approach using gas mixing furnaces to investigate the effect of Ti oxide formation at different f O 2 on Ti stable isotope fractionation during mare basalt petrogenesis. Two identical bulk compositions were equilibrated simultaneously during each experiment to guarantee comparability. One experiment was investigated with the EPMA to characterize the petrology of experimental run products, whereas the second experiment was crushed, and fabricated phases (i.e., oxides, silicates and glass) were handpicked, separated and digested. An aliquot of each s le was mixed with a Ti double-spike, before Ti was separated from matrix and interfering elements using a modified HFSE chemistry. Our study shows f O 2 -dependent fractionation within seven s les from air to IW-1, especially ∆ 49 Ti armalcolite-melt and ∆ 49 Ti armalcolite-orthopyroxene become more fractionated from oxidized to reduced conditions (− 0.092 ± 0.028- − 0.200 ± 0.033 ‰ and − 0.089 ± 0.027- − 0.250 ± 0.049 ‰, respectively), whereas ∆ 49 Ti orthopyroxene-melt shows only a minor fractionation (− 0.002 ± 0.017-0.050 ± 0.025 ‰). The results of this study show that Ti isotope fractionation during mare basalt petrogenesis is expected to be redox dependent and mineral-melt fractionation as commonly determined for terrestrial f O 2 may not be directly applied to a lunar setting. This is important for the evaluation of Ti isotope fractionation resulting from lunar magmatism, which takes place under more reducing conditions compared to the more oxidized terrestrial magmatism.
Publisher: Springer Science and Business Media LLC
Date: 02-12-2011
Publisher: Springer Science and Business Media LLC
Date: 16-11-2017
Publisher: Springer Science and Business Media LLC
Date: 29-07-2019
Publisher: SPIE
Date: 13-12-2020
DOI: 10.1117/12.2561505
Publisher: Springer Science and Business Media LLC
Date: 23-05-2017
Publisher: Mineralogical Society of America
Date: 04-2017
Publisher: Wiley
Date: 17-09-2021
Publisher: Springer Science and Business Media LLC
Date: 08-2022
DOI: 10.1007/S00410-022-01947-0
Abstract: In terrestrial magmas titanium is predominantly tetravalent (Ti 4+ ), in contrast, lunar magmas are more reduced (IW-1) and hence approximately 10% of their bulk Ti content is trivalent (Ti 3+ ). Changes in oxidation state and coordination number are both important parameters that can serve to drive Ti stable isotope fractionation. As such, mineral–mineral and mineral-melt Ti stable isotope fractionation factors determined for terrestrial s les may not be appropriate for lunar s les that formed under more reducing conditions. To address this issue, several experiments were carried out in gas mixing furnaces over a range of f O 2 (air to IW-1) to determine Ti stable isotope fractionation factors for minerals, such as ilmenite, clinopyroxene and rutile that are highly abundant on the Moon. Results show that the extent of Ti stable isotope fractionation significantly increases with decreasing f O 2 . For ex le, the isotopic difference between ilmenite and residual melt (Δ 49 Ti ilmenite-melt ) is resolvably lower by ~ 0.44 ‰ from terrestrial-like FMQ-0.5 to lunar-like IW-1 at an intermediate precision of ± 0.003 ‰ (95% c.i. OL–Ti). This confirms that fractionation factors determined for terrestrial conditions are indeed not applicable to lunar settings. Our new fractionation factors for ilmenite, clinopyroxene and silicate melt are mostly consistent with those previously determined by ab initio modelling based on density-functional theory. Using our new experimental data in conjunction with previously published high-precision HFSE data and Ti stable isotope data of lunar basalts, we modelled the solidification of the Lunar Magma Ocean (LMO). The model for LMO solidification included fractionation of Ti stable isotopes not only by Ti-oxides, but also by typical lunar silicate minerals as pyroxene or olivine. The resulting δ 49 Ti for urKREEP and ilmenite-bearing cumulates are within error of previous estimates, but also indicate that ilmenite-bearing cumulates must have contained around 15% ilmenite.
Publisher: Springer Science and Business Media LLC
Date: 20-11-2018
Publisher: Mineralogical Society of America
Date: 12-2020
DOI: 10.2138/AM-2020-7477
Abstract: Evidence of immiscibility between arsenide and sulfide melts has been observed both in experimental studies and natural s les from several localities worldwide (e.g., Ronda, Spain Beni Bousera, Morocco Dundonald Beach South, Canada). Platinum-group elements (PGE) have shown to have a strong affinity for arsenide melts, but little is known about their partitioning behavior between arsenide and sulfide melts. In this study, we experimentally determine the partition coefficients of PGE (Pt, Pd, Ir, Ru, and Os) between both types of melt in As-saturated sulfide systems doped with trace amounts of PGE. Results show that all PGE display a strong preference to the arsenide melt with DPGEAs/sulf melts ranging from 20 to 2700, with Ir and Pt showing a marked preference for arsenide melts. These partition coefficients values are similar to estimates made from natural s les and demonstrate that the separation of arsenide melts from sulfide magmas can be an efficient mechanism to scavenge PGE from magmas and to fractionate Os, Ru, and Pd from Pt and Ir.
Publisher: Wiley
Date: 06-10-2022
DOI: 10.1111/JMG.12634
Abstract: High‐ and ultrahigh‐pressure rocks occur in the Austroalpine Nappes in a ~400 km long belt from the Texel Complex in the west to the Sieggraben Unit in the east. Garnet growth during pressure increase was dated using Lu‐Hf chronometry. The results range between c. 100 and 90 Ma, indicating a short‐lived period of subduction. Combined with already published data, our estimates of metamorphic conditions indicate a field gradient with increasing pressure and temperature from the northwest to the southeast, where the rocks experienced ultrahigh‐pressure metamorphism. The P‐T conditions of the eclogites generally lie on the ‘warm’ side of the global range of subduction‐zone metamorphic conditions. The oldest Cretaceous eclogites (c. 100 Ma) are found in the Saualpe‐Koralpe area derived from widespread gabbros formed during Permian to Triassic rifting. In the Texel Complex garnets showing two growth phases yielded a Variscan‐Eoalpine mixed age indicating re‐subduction of Variscan eclogite‐bearing continental crust during the Eoalpine orogeny. Jurassic blueschist‐facies metamorphism at Meliata in the Western Carpathians and Cretaceous eclogite‐facies metamorphism in the Austroalpine are separated by a time gap of c. 50 Ma and therefore do not represent a transition from oceanic to continental subduction but rather separate events. Thus, we propose that subduction initiation was intracontinental at the site of a Permian rift.
Publisher: FapUNIFESP (SciELO)
Date: 12-2014
DOI: 10.1590/0001-3765201420140014
Abstract: Subduction zone or arc magmas are known to display a characteristic depletion of High Field Strength Elements (HFSE) relative to other similarly incompatible elements, which can be attributed to the presence of the accessory mineral rutile (TiO2) in the residual slab. Here we show that the partitioning behavior of vanadium between rutile and silicate melt varies from incompatible (∼0.1) to compatible (∼18) as a function of oxygen fugacity. We also confirm that the HFSE are compatible in rutile, with D(Ta) D(Nb) (D(Hf) /∼ D(Zr), but that the level of compatibility is strongly dependent on melt composition, with partition coefficients increasing about one order of magnitude with increasing melt polymerization (or decreasing basicity). Our partitioning results also indicate that residual rutile may fractionate U from Th due to the contrasting (over 2 orders of magnitude) partitioning between these two elements. We confirm that, in addition to the HFSE, Cr, Cu, Zn and W are compatible in rutile at all oxygen fugacity conditions.
Publisher: Elsevier BV
Date: 02-2008
Publisher: Springer Science and Business Media LLC
Date: 16-02-2018
Publisher: Elsevier BV
Date: 11-2017
Publisher: Geological Society of America
Date: 05-02-2016
DOI: 10.1130/G37545.1
Publisher: Elsevier BV
Date: 10-2015
Publisher: Springer Science and Business Media LLC
Date: 23-05-2017
Publisher: Elsevier BV
Date: 11-2016
Publisher: Elsevier BV
Date: 08-2016
Publisher: Copernicus GmbH
Date: 14-07-2021
Abstract: Abstract. An electrum–quartz pebble with a weight of 10.4 g was discovered in a cliff of Saalian glaciogenic sediments on the west coast of the German North Sea island of Sylt in 2012. It has a roundish water-worn appearance and consists of intergrown electrum and milky quartz. It is the largest known electrum find in Germany, and regarding its weight it also ranks amongst the largest gold finds discovered in Germany. We document and characterize this unusual discovery. Furthermore, an attempt is made to investigate its provenance. Therefore, reference s les of southern Scandinavian gold and electrum deposits and occurrences have been studied and compared to the Sylt find. The Au–Ag content determined by electron microprobe (EMP), trace element signature measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and Pb isotope compositions by multi-collector ICP MS (MC-ICP-MS) suggest a southern Norwegian origin. The most probable source might be the Kongsberg ore district or an adjacent, yet undiscovered, mineralization in the Oslo region. In general, Saalian glaciogenic sediments in Schleswig-Holstein (northern Germany) are dominated by rocks of Swedish provenance. Due to the intake of older Elsterian sediments by younger Saalian glaciers, southern Norwegian rocks are also not uncommon in Saalian sediments. A Saalian ice advance or a combination of Elsterian and Saalian ice advances might have provided a transport mechanism for an electrum s le from a south Norwegian mineralization to the island of Sylt.
Publisher: Springer Science and Business Media LLC
Date: 11-04-2019
Publisher: Elsevier BV
Date: 08-2018
Publisher: Springer Science and Business Media LLC
Date: 22-04-2013
Publisher: Elsevier BV
Date: 06-2020
Publisher: Elsevier BV
Date: 06-2015
Publisher: Brill
Date: 20-06-2017
DOI: 10.1163/15718182-02501007
Abstract: As at March 2016, 49 states had reformed their laws to clearly prohibit all corporal punishment of children (United Nations 1989) in all settings, including the home (Global Initiative to End All Corporal Punishment of Children, n.d.) By January 2017 this number had reached 52. As the trend moves towards abolition, it is not an acceptable position for the United Kingdom ( uk ), the United States of America ( usa ) and Australia (Poulsen, 2015) to remain missing from that list. Whilst they are, effectively, a child (a person aged under 18 years of age), is the only person in all three countries that it is legal to hit. This article seeks to restate arguments in this area in a simple way to restart the debate in a modern context where understanding of child abuse is perhaps more widespread than it ever was in the past. On 20 October 2014 a report, Living on a Railway Line, was launched in the uk to mark the 25th anniversary of the signing of the un Convention on the Rights of the Child, which took place on 20 November 1989 (Rowland, 2014). It recommended removing the defence of reasonable chastisement in relation to the punishment of children. This article seeks to build on that agenda in a comparative context taking a three way perspective from the uk , the usa and Australia. It concludes that moves to prevent family violence are progressive but the position of a society where physical punishment of children is permitted yet child abuse is forbidden is not a tenable one. Reducing the number of cases of child abuse must begin with a clear message from society that physical punishment of children, whatever the circumstances, is unacceptable. The situation is serious enough to introduce aspirational legislation to remove justifications for physical punishment of children with the aim of modifying behaviour within society.
Publisher: Springer Science and Business Media LLC
Date: 17-06-2020
Publisher: Mineralogical Society of America
Date: 07-2021
DOI: 10.2138/AM-2021-7612
Abstract: Several recent papers have purported to find ultra-reduced minerals—as natural ex les—within ophiolitic mantle sections, including SiC moissanite, Fe-Si alloys, various metal carbides, nitrides, and borides. All those phases were interpreted to be mantle derived. The phases are recovered from mineral concentrates and are assigned to the deep mantle because microdiamonds and other ultrahigh-pressure (UHP) minerals are also found. Based on these findings, it is claimed that the mantle rocks of ophiolite complexes are rooted in the transition zone (TZ) or even in the lower mantle, at redox states so reduced that phases like SiC moissanite are stable. We challenge this view. We report high-temperature experiments carried out to define the conditions under which SiC can be stable in Earth’s mantle. Mineral separates from a fertile lherzolite xenolith of the Eifel and chromite from the LG-1 seam of the Bushveld complex were reacted with SiC at 1600 K and 0.7 GPa. At high temperature, a redox gradient is quickly established between the silicate/oxide assemblage and SiC, of ~12 log-bar units in fO2. Reactions taking place in this redox gradient allow us to derive a model composition of an ultra-reduced mantle by extrapolating phase compositions to 8 log units below the iron-wüstite equilibrium (IW-8) where SiC should be stable. At IW-8 silicate and oxide phases would be pure MgO end-members. Mantle lithologies at IW-8 would be Fe° metal saturated, would be significantly enriched in SiO2, and all transition elements with the slightest siderophile affinities would be dissolved in a metal phase. Except for the redox-insensitive MgAl2O4 end-member, spinel would be unstable. Relative to an oxidized mantle at the fayalite-magnetite-quartz (FMQ) buffer, an ultra-reduced mantle would be enriched in enstatite by factor 1.5 since the reduction of the fayalite and ferrosilite components releases SiO2. That mantle composition is unlike any natural mantle lithology ever reported in the literature. Phases as reduced as SiC or Fe-Si alloys are unstable in an FeO-bearing, hot, convecting mantle. Based on our results, we advise against questioning existing models of ophiolite genesis because of accessory diamonds and ultra-reduced phases of doubtful origin.
Publisher: Elsevier BV
Date: 10-2009
Publisher: Oxford University Press (OUP)
Date: 08-2022
DOI: 10.1093/PETROLOGY/EGAC067
Abstract: It is not well known which chemical differentiation pathways basaltic melts will take when they are iron metal saturated. Thermodynamically, the pathway seems predictable. So long as Fe metal is a stable liquidus phase and relative oxygen fugacity (fO2) is not subject to major fluctuations, the activity of FeO (aFeOmelt) is buffered by the iron–wüstite (IW) equilibrium 2Femetal + O2 → 2FeOmelt. Metallic Fe also stabilizes olivine through the equilibrium 2Femetal + O2 + SiO2 melt → Fe2SiO4 olivine. That equilibrium tends to suppress the enrichment in bulk SiO2 when Fe saturated basaltic melts differentiate. We document the differentiation history of tholeiitic cumulates from the Siberian craton that carry up to 30 modal % metallic Fe. Our study is complemented by differentiation experiments at two redox states, one set in Fe metal capsules at 1.6 log units below IW (IW-1.6) and a second set in graphite capsules at IW + 1.5. Iron saturated differentiation pathways do not show enrichments in FeO nor in bulk SiO2 because olivine remains stable along the entire liquid line of descent. By contrast, melts equilibrated at IW + 1.5, that is, outside metallic Fe saturation, crystallize pigeonite as first silicate and follow a normal (terrestrial) differentiation pathway involving marked SiO2 enrichment. The Fe-saturated path duplicates in detail the liquid line of descent we derive for the cumulates. Iron-saturated experiments have limited applicability to the Earth because there are so few terrestrial basalts saturated with metallic Fe however, they might apply to the Moon. Many lunar basalts appear to have been saturated with an Fe-Ni phase during their emplacement on the lunar surface, and potentially during generation within the lunar mantle.
Publisher: Elsevier BV
Date: 09-2017
No related grants have been discovered for Raúl O. C. Fonseca.